Generally in electrostatographic reproduction, the original to be copied is rendered in the form of a latent electrostatic image on a photosensitive member. This latent image is made visible by the application of electrically charged toner.
The toner forming the image is transferred to a substrate, also referred to in the art as a “receiver”, such as paper or transparent film, and fixed or fused to the substrate. Where heat softenable toners, for example, thermoplastic polymeric binders, are employed, the usual method of fixing the toner to the substrate involves applying heat to the toner once it is on the substrate surface, to soften it and then permitting or causing the toner to cool. This application of heat in the fusing process is at a preferred temperature of about 90° C.-220° C.; pressure can be employed in conjunction with the heat.
A system or assembly for providing the requisite heat and pressure is generally provided as a fusing subsystem, and customarily includes a fuser member and a support member. The various members that make up the fusing subsystem are considered to be fusing members; of these, the fuser member is the particular member that contacts the toner to be fused by the fusing subsystem. The heat energy employed in the fusing process is generally transmitted to toner on the substrate by the fuser member. Specifically, the fuser member is heated to transfer heat energy to toner situated on a surface of the substrate. The fuser member contacts this toner, and correspondingly also can contact this surface of the substrate itself. The support member contacts an opposing surface of the substrate.
Accordingly, the substrate can be situated or positioned between the fuser and support members so that these members can act together on the substrate to provide the requisite pressure in the fusing process. In cooperating, preferably the fuser and support members define a nip, or contact arc, through which the substrate passes. Preferably, the fuser and support members are in the form of fuser and pressure rollers, respectively. Yet additionally one or both of the fuser and support members have a soft layer that increases the nip to effect better transfer of heat to fuse the toner.
During the fusing process toner can be offset from the substrate to the fuser member. Toner transferred to the fuser member in turn can be passed on to other members in the electrostatographic apparatus or to subsequent substrates subjected to fusing. Toner on the fusing member therefore can interfere with the operation of the electrostatographic apparatus and with the quality of the ultimate product of the electrostatographic process. This offset toner is accordingly regarded as contamination of the fuser member, and preventing or at least minimizing this contamination is a desirable objective
Release agents are frequently applied to fusing members during the fusing process, to combat toner offset. These agents usually are or include polyorgano-siloxanes, particularly polyorganosiloxane oils. The polysiloxanes have antiadhesive properties that are favorable for protecting the surface of the fuser member, and maintaining the durability of the fuser member. Release agents are most effective when applied in a uniform, continuous layer, as can be achieved with a donor roller oiler.
A donor roller oiler includes two rollers and a metering blade, which can be a rubber, plastic, or metal blade. One roller meters the oil in conjunction with the blade, and the other transfers the oil to the fuser roller. The roller transferring the oil to the fuser, or donor roller, is usually a compliant cushioned roller. This type of oiler is common in the art, and is frequently used with fuser members having fluoroelastomer fusing surface layers.
The compliant cushioned donor roller must provide a uniform layer of release agent while preventing toner contamination on the fuser roller from collecting on the other oiler components. It is desirable that the roller have a long life and be low cost to manufacture.
According to prior art techniques the toner release agents can be applied to the fuser roller by way of a release agent donor roller which can include an EPDM (terpolymer elastomer made from ethylene, propylene and diene monomer) core with a thin sleeve of Teflon, PFA (E.I. DuPont De Nemours) which is an independent extruded thin sleeve of material which is bonded onto the core.
The use of such a sleeve is very expensive and the manufacturing of such a donor roll, is tedious and inefficient, the yield being relatively low since so many of the sleeves are damaged during manufacture. Furthermore, in a fusing assembly such as that illustrated in FIG. 1, which will be described in greater detail hereinafter, such a sleeved release agent donor roller is ineffective in that since the release agent donor roller is driven by frictional engagement with the fuser roll, the hard Teflon PFA coating has a relatively low coefficient of friction difficulties are presented in providing the necessary driving component. Additionally, unless expensive fluorosurfactants or fluorosilicones are employed, the release fluid does not wet the fluorocarbon surface and this causes non-uniform oil delivery.
Another technique has been with the use of a release agent donor roller made of a high temperature vulcanized silicone rubber material. Another development is described in U.S. Pat. No. 4,659,621 to Finn et al. wherein a release agent donor roller is described as having a conformable donor surface including the crosslinked product of at least one addition curable vinyl terminated or vinyl pendant polyorganosiloxane, a polyfunctional silicone hydride crosslinking agent crosslinking catalyst and finely divided filler. While these silicone elastomer donor rolls have been commercially successful in some commercial applications they suffer from certain difficulties in that they tend to swell by being in contact with a silicone oil release agent which migrates or is absorbed into the silicone rubber. While a small degree of swelling can be acceptable if it is uniform, failure of such rolls has been observed by excessive swelling over a period of operation wherein the release agent donor roller can actually be twice the original size. Under such circumstances, the silicone rubber release agent donor roller can no longer function in providing a uniform layer of release fluid to the fuser roll.
Another recent development is described in U.S. Pat. No. 5,061,965 to Ferguson et al. This describes the use of a release agent donor roller made of a base roller, an intermediate comfortable silicone elastomer layer, and an elastomer release layer including poly(vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene) where the vinylidene fluoride is present in an amount <40 mole %, a metal oxide present in an amount sufficient to interact with polymeric release agent having functional groups to transport a sufficient amount of polymeric release agent to provide an interfacial barrier layer between the fusing surface and the toner. This release agent donor roller suffers from the polymeric release agent wetting capability between the nonfunctional PDMS release agent and the nonreactive release agent donor roller surface since the invention counts on the polymeric release agent having functional groups to react with the metal oxide which is dispersed in the fluoroelastomer layer.
A more recent development described in U.S. Pat. Nos. 5,141,788 and 5,166,031 to S. Badesha wherein a release agent donor roller including a supporting substrate having an outer layer of a surface grafted or volume grafted polyorganosiloxane formed by dehydrofluorination of the fluoroelastomer by nucleophilic dehydrofluorinating agent, followed by addition polymerization by the addition of an alkene functionalized polyorganosiloxane and a polymerization initiator. Fabricated release agent donor roller used for supplying conventional silicone oil release agent showing 4.3 million copies without failure. Although these rolls provide long life, non-oil swelling, and can be used with non-functional PDMS release agent, the manufacturing of such a release agent donor roller is tedious, inefficient, and expensive.
Another more recent development is described in U.S. Pat. No. 6,190,771 to Chen et. al. wherein a silicone donor roller is prepared that has a controlled swell. Although these rolls provide reduced impact of oil swelling and can be used with non-functional PDMS release agent, the rollers oil compatibility is reduced and thus the ability to resist toner contamination is impaired.
It would be desirable to have a simple donor roller that would effectively resist toner contamination while being resistant to the effects of oil swell. It would further be desirable that it is simple and low cost to manufacture.